This is a multi-centered protocol to screen for patients at high risk of becoming type I diabetics, and to intervene with treatment to attempt to prevent the development of diabetes. It has recently become possible using islet cell autoantibodies (ICA) to identify individuals who have a 50 percent chance of developing IDDM within the next 5 years. Primary relatives of patients with IDDM have a tenfold increased risk of having ICA and this is the group that will be targeted in this trial. Patients who are classified as intermediate risk or high risk for developing IDDM will be offered one of two randomized intervention protocols. Those patients in the high risk category (greater than 50 percent of developing IDDM over the next 5 years) will be offered a randomized trial of no treatment versus daily subcutaneous injections of long-acting insulin. There are three separate stages of this study, each of which have separate objectives: STEP 1: SCREENING: Initial eligibility screening of relatives for IDDM risk by determining ICA. STEP II: STAGING: Definition of risk categorized by staging of ICA positive patients as to the risk of developing clinical IDDM. STEP III: INTERVENTION: Implementation of the insulin intervention protocol for patients in the high risk category. Patients that are in step 2 or step 3 will be studied in the General Clinical Research Center at University Hospitals.